Kirby_1983_J.Mol.Cell.Cardiol_15_685

The development of muscarinic acetylcholine receptors in chick heart was studied from incubation days 5 through 20. There is a parallel increase in receptor density in atrium and ventricle until the last half of incubation, when the atrial, but not the ventricular, receptor density increases. This increase is blocked by exposure to atropine on incubation days 11 through 14, but not on days 16 through 19. This specific regional increase is coincident with the appearance of functional cholinergic innervation of the heart. During this same period there is an alteration in muscarinic receptor binding properties in both atrium and ventricle that is characterized by an increase in the proportion of receptors displaying high affinity agonist binding. This increase is blocked in the atrium, but not the ventricle, by atropine exposure on incubation days 11 through 14. Thus, there is a critical period in the development of atrial muscarinic receptors during which the receptors are susceptible to modulation by exposure to an antagonist.